This invention relates generally to a cover belt for a duct, made of a flexibly deformable material with metallic reinforcements. More particularly, this invention relates to a cover belt for a duct receiving electric cables or busbars for the power supply of a movable energy user, for example, a transporter bridge or quayside crane. This cover belt can be swung up from a closed position by a deflecting device on the movable energy user and then afterwards falls back into its closed position behind this same deflecting device.
The traditional method of feeding electrical power to quayside cranes through contact rails has now virtually been superseded by cable systems. However it is still necessary to provide protection for the cable from quay traffic. Furthermore, safety regulations in many ports require some form of housing. The simplest and most economic method is to provide an open duct, although this is a hazard to pedestrians and can easily become clogged by debris, possibly damaging the cable. A more sophisticated solution is to cover the duct with hinged metal plates. This system however, suffers many drawbacks since maintenance requirements are considerable. Moreover, the complex design of the plate lifting mechanism slows transit speed of the crane.
A semi-flexible cover belt is known in the prior art from DE-A-3005454. A deflecting device on the energy user creates a local opening of the semi-flexible cover belt during movement of the energy user, by twisting the belt by means of deflecting elements on the deflecting device. Behind the deflecting device the belt is again closed by resilient deformation and the belt's own dead weight. A device of this type thus permits unhindered winding and unwinding of an electric cable laid in the duct or, in the case of busbars, unhindered introduction of a current collector into the duct. At the same time the continuous cover belt ensures excellent protection of the cable and/or busbar in the duct against the affects of weather and debris. In addition, unhindered movement of vehicles over the duct is always ensured.
The belt disclosed in DE-A-3005454 consists of a flexibly deformable rubber material in which metallic reinforcements are embedded. It comprises a securing strip, a joint strip and a cover strip. The securing strip is secured along a first longitudinal edge of the duct. The joint strip flexibly connects the securing strip to the cover strip. The cover strip spans the duct and rests on both sides of the duct.
It is quite clear that the design of the reinforcement of the cover belt is a particularly important feature for the proper function of this belt. In a cover belt in accordance with DE-A-3005454, this reinforcement consists of three different layers of metallic reinforcements embedded in the flexibly deformable rubber material. A first layer consists of stranded steel wires near the underside of the belt. These first stranded steel wires run parallel to and across the longitudinal direction of the cover belt over the full width of the cover belt. A second layer likewise consists of stranded steel wires running parallel to and across the longitudinal direction of the cover belt. These second stranded steel wires are arranged exclusively near the topside of the cover strip. A third layer consists of a semi-rigid reinforcement which is provided in the cover strip between the first and second reinforcement.
Excellent results have been achieved with this special reinforcement in practice. The cover strip spanning the duct is dimensionally stable in the transverse direction and always returns to its flat position when closed after twisting during opening, so that its free edge lies flat in a recess at the edge of the duct and is thus protected from traffic passing over the duct. In the longitudinal direction, the cover belt is flexible enough to allow it to be twisted when opened, but at the same time is sufficiently dimensionally stable to prevent development of undulating longitudinal deformation of the cover belt. In the area of the joint strip, the first reinforcing layer ensures the required flexibility and at the same time strength to prevent fractures of the cover belt in this heavily stressed area. The high rigidity achieved by the second and third reinforcing layers, which are arranged exclusively in the area of the cover strip, permits easy support of vehicular traffic and prevents sagging of the cover belt in the area of the cover strip during opening. There is thus no risk that the cover belt could slip off the deflecting device as a result of transverse deformation of the cover strip.
A disadvantage of the otherwise excellent cover belt disclosed in DE-A-3005454 is that tears do occur in the securing strip, particularly when the belt is exposed to extreme loads due to heavy traffic both in weight and in volume.
An attempt was made to strengthen the reinforcing strip of the cover belt in accordance with DE-A-3005454 by adding additional metallic reinforcements. Apart from the fact that the existing material thickness of the cover belt in the area of the reinforcing strip allows very little free space for embedding further metallic reinforcements, it has been discovered that these additional metallic reinforcements have a negative affect on the dimensional stability of the cover belt. In the closed position, the cover strip was no longer in the required flat position. Attempts to strengthen the securing strip by textile reinforcements produced similar negative results in regard to the flat position of the cover belt.
It is clear as a result of the foregoing discussion that despite the many good features of the prior art as disclosed in DE-A-3005454, there is a need to provide a reinforced cover belt which has a securing strip which is much less sensitive to tearing, distortion and/or damage than that of the prior art.